Hello,

The most important step in order to secure good marks are being well acquainted with the syllabus and your books, in case you have CBSE Board you should pay importance to NCERT books first in that case, be through with its, go through previous  year paper of sample papers, making a time table helps in this case, you can accordingly assign number of hours to the subject, analyze your weakness and strength, and try to work on the areas that need your utmost attention at the same time don't neglect your areas of strength, but most importantly have a positive mindset and right attitude, board exams can really be stressful, so you should also take good care of your health, do meditation as well as yoga for your well being, in case of any doubts ask your teacher for the same, in order to achieve anything in life requires an immense focus, dedication and sincerity, so try to give your best for instance take regular test to analyze your preparation level, and compete with yourself only in order to better yourself than earlier.